1. Field of the Invention
The present invention relates to a cylinder apparatus capable of clamping a workpiece by the aid of an arm which is rotatable by a predetermined angle in accordance with a displacing action of a piston.
2. Description of the Related Art
When components of an automobile are welded, for example, a cylinder apparatus has been hitherto used to clamp such a component. The cylinder apparatus is disclosed, for example, in U.S. Pat. No. 4,905,973 and DE 29504267 U1.
The cylinder apparatus disclosed in U.S. Pat. No. 4,905,973 and DE 29504267 U1 comprises a main body which is constructed by integrally assembling a pair of casings formed to be substantially symmetrical to one another, a cylinder unit which is connected to the main body, and an arm which is rotatable by a predetermined angle in accordance with a driving action of the cylinder unit by the aid of a toggle link mechanism provided in the main body.
The cylinder unit is provided with a piston which is reciprocatively accommodated in a cylinder tube, and a piston rod which is connected to the piston. The toggle link mechanism, which comprises a bearing member for rotating the arm, is connected to a free end of the piston rod. A guide groove is formed on an inner wall surface of the casing, which functions to guide the linearly movable piston and absorb the reaction force applied when a workpiece is clamped by the arm.
A desired welding operation is performed for the workpiece while clamping the workpiece by the aid of the arm which is rotatable by a predetermined angle in accordance with the driving action of the cylinder unit.
However, the cylinder apparatus disclosed in U.S. Pat. No. 4,905,973 and DE 29504267 U1 adopts an arrangement in which the reaction force is applied to the arm when the workpiece is clamped by the arm, and the reaction force is received by the guide groove formed on the inner wall surface of the casing. In this arrangement, the wall surface for constructing the guide groove wears out due to sliding friction of the piston rod which is reciprocated integrally with the piston. Therefore, backlash or looseness occurs resulting from a gap between the piston rod and the guide groove, and it becomes difficult to rotate the arm in a stable manner. Further, a disadvantage arises in that the occurrence of backlash decreases the clamping force of the arm for the workpiece.